GASTEEOPODA. 147 



large and tliick, like haliotis, but entii-ely covered by the thick, bard, plaited 

 mautle of the animal. 



Stomatia (Helblifl), Lamarck. 

 Etym., stoma, the apertm-e. 

 Ty2)e, S. phymotis, PI. X., fig. 22. 



Shell like haliotis, but without perforations, their place being occupied by 

 a simple furrow ; sm-face rugose, spirally ridged ; spire small, prominent 

 aperture large, oblong, outer margin iiTegular. 



Distr., 12 sp. Java, Philippines, Torres Straits, Pacific. Under stones 

 at low water (Cuming). 



Fossil. M. D'Orbigny refers to this genus 18 sp., ranging from the L. 

 Silurian to the chalk, N. America, Em-ope. 



SCISSURELLA, D'Orb. 

 Eti/m.., diminutive of scissus, slit. 



Tf/pe, S. crispata, PI. X., fig. 23. Syn., anatomus, IMontf. 

 Shell minute, thin, not pearly ; body-whirl large ; spire small ; surface 

 striated ; apertm-e rounded, with a slit in the margin of the outer lip. Oper- 

 \< culate. 



Distr., 5 sp. Norway, Brit., Medit. In 7 fathoms water off the Orkneys, 

 and in deep water east of the Zetland Isles. 

 Fossil, 4 sp. Miocene — . Brit., Sicily. 



Pleueotomaria, Defrance. 

 Etf/m., pletcra, side, and tome, notch. 

 Type, P. anglica, PI. X., fig. 24. 



Shell, trochiform, solid, few-whirled, Tivith the sm-face variously ornamented ; 



apertm-e sub-quadi-ate, with a deep slit iu its outer margin. The part of the 



slit which has been progressively filled up, forms a band round the whirls. 



Fossil, 400 sp. Lower silm-iau — chalk. N. America, Europe, Australia. 



} Specimens from clay strata retain their nacreous inner layers, those fi-om the 



, chalk and limestones have lost them, or they are replaced by crystalline spar. 



t Pleurotomarifc with wavy bands of colour have been obtained in the carb. 



i limestone of Laucashire. In this extensive group there are some species 



[ which rival the living turbines in magnitude and solidity, whilst others are as 



i frail as ianthina. 



Sub-ffem(S. Scalites, Conrad (= raphistoma. Hall.) E.g., S. angulatus 



and stamineus. L. silm-ian. New York. Shell thin ; whirls angular, fiat 



, above (tabulated), 8 sp. L. silm-ian — carb. Foly-tremaria, D'Orb., is 



i founded on P. catenata, Koninck, in which the margins of the slit are wavy, 



t-'onverting it into a series of perforations. 



MuRCHisoNiA, D'Archiac. 

 Etym., named in honom- of Sir Roderick I. Mm-chison. 

 Type, M, bilineata. PL X., fig. 25. 



